Tissue slices, cellular toxicity

During preclinical development the metabolite structures of potential new drug candidates are typically identified via in vitro tools such as subcellular liver fractions (microsomes, S9), expressed human enzymes, or cellular systems (e.g., hepatocytes, tissue slices) [25]. The metabolism observed in the different systems is compared across species, with the aim that all the metabolites formed in human in vitro systems can also be identified in the systems originating from the animal species used in major toxicity studies. 

In the past decades, there has been a large increase in the development and use of in vitro models, not only because of the demand of animal welkre groups to reduce the use of laboratory animals, but also because of a number of scientific and financial advantages. Especially in the case of small laboratory animals, a number of different models have become available for biotransformation and toxicity studies, e,g, perfused organs, tissue slices, isolated cells (e,g, hepatocytes), cellular fractions (e.g. microsomes), and purified enzymes. For a number of reasons (see below) isolated hepatocytes have become one of the most popular in vitro models for such studies. 

Although the emphasis of this chapter is on isolated cells in culture, responses at the cellular level can be assessed in intact tissue after exposure of the whole animal. Observations of cellular responses are most often made with in situ detection techniques and microscopic observation, such as immunohistochemisty (Chapter 7) and nucleic acid hybridization (Chapter 2). Preparations used for these in situ techniques are generally tissue that has been fixed after toxicant treatment, then embedded and sliced thinly enough (-5 pm) to enable observation by microscopy, usually... 

Azri and coworkers (1990) have investigated carbon tetrachloride-induced hepato-toxicity in rat liver slices. Liver slices from male rats were incubated and exposed to carbon tetrachloride vapors, and the degree of injury to cellular tissue was determined. Covalent binding of CCU radical to proteins and lipid molecules in a slice caused the cellular injury. The toxicity depended on the vapor concentration and the time of exposure. Azri and coworkers reported further that rats pretreated with phenobarbital were more rapidly intoxicated even at a lower concentration of carbon tetrachloride vapors. On the other hand, pretreatment with allyliso-propylacetamide inhibited the toxicity of carbon tetrachloride. 

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